分光光度法测定自来水中的镁

分光光度法测定自来水中的镁

摘要

本实验是应用分光光度法测定自来水中镁含量。在pH值为10的氨水-氯化铵碱性缓冲液中，以MTB（甲基百里香酚蓝）作为显色剂，镁与MTB生成稳定的蓝紫色络合物，其吸光度与镁含量在一定浓度范围内成正比。在室温条件下，用721B型分光光度计，在602nm波长处、4mLpH值为10的氨水-氯化铵碱性缓冲液、3mL的MTB(0.3784μg/mL)溶液、显色时间8分钟测定吸光度，络合物的吸光度达到最大值并且相对稳定。实验结果表明：镁浓度在1.00~5.00ug·mL-1呈良好的线性关系得到标准曲线的线性回归方程为y=0.0632x+0.1626（x：镁含量，y：吸光度），相关系数为0．9995，摩尔吸光系数为1.79×104L/mol·cm，实验对16种干扰离子进行了考察，发现标准偏差在 5%范围外的有钙、锌2种离子对镁测定结果存在较大干扰，加入EGTA（乙二醇二乙醚二胺四乙酸）和六次甲基四胺为掩蔽剂，可以分别消除钙离子和锌离子的干扰。最后试验测得自来水中镁离子含量为28.25g/L,平均回收为99.63%，镁离子测定比较准确。

关键词：分光光度法，镁，MTB，自来水,EGTA，六次甲基四胺

SPECTROPHOTOMETRIC METHOD FOR

DETERMINATION OF WATER MAGNESIUM

Abstract

a method for determining in magnesium content in water with spectrophotometry is proposed in this paper. MTB is selected as the chromomeric reagent. Magnesium and MTB generate amaranth complex. In the medium(pH=10) of Ammonium Hydroxide–ammonium chloride acetate, magnesium combined with MTB to form a stable quaternion – mixed micelles system with the existence of polyethylene glycol The absorbency was direct proportion to the content of magnesium in a certain range of concentration. It has been determined the wavelength of maximum absorption is 602nm. At room temperature, with 721 type spectrophotometer to measure spectrophotometry, through the experiment determination of the stability and reproducibility worse after the test, 5×10-4 μg mL-1 the MTB in solution 3 mL sensitive, and measure the highest when at room temperature, show color time after 8 minutes, in the pH value of 10 Ammonium Hydroxide–ammonium chloride alkaline solution in the complex, the absorbency and reach a maximum relatively stable. The experimental results show that: magnesium concentration in 1.00 ~5.00ug/mL is good linear relationship between the get standard curve of the linear regression equation is Y=0.0632X+0.1626, correlation coefficient is 0.9915, the molar absorption coefficient is 7.1 ×4

10L / mol·cm, molar absorption coefficient is 7.1 ×4

10L/mol·cm, experiments on 16 ion of jamming in the determination, the author finds that there were seven allowed for magnesium determination result in bigger interference, join EGTA and methenamine as masking agent can remove interference, other ion to the magnesium ion determination are in the allowable value range.Magnesium ions in the final tests measured water content of

28.25g/L, an average recovery of 99.63%, magnesium ion content more accurately. Keyword:spectrophotometry ,magnesium, MTB , water,EGTA

目录

前言 (1)

1 实验部分 (2)

1.1实验原理 (2)

1.2主要仪器与试剂 (4)

1.2.1仪器 (4)

1.2.2试剂和标准样的配制 (4)

1.2.3 721B分光光度计仪器的结构及操作事项 (5)

1.3样品取样 (7)

2 结果与讨论 (8)

2.1最佳实验条件选择 (8)

2.1.1测定最大吸收波长 (8)

2.1.2显色剂的用量选择 (9)

2.1.3显色时间的考察 (9)

2.1.4缓冲溶液的考察 (10)

2.3干扰离子的考察 (12)

2.3.1钡离子的干扰考察 (13)

2.3.2钠离子的干扰考察 (13)

2.3.3钾离子的干扰考察 (14)

2.3.4锶离子的干扰考察 (14)

2.3.6铬离子的干扰考察 (15)

2.3.7磷离子的干扰考察 (15)

2.3.8锰离子的干扰考察 (16)

2.3.9锌离子的干扰考察 (16)